Wireless communication techniques based on multiple subcarriers, such as an orthogonal frequency-division multiplexing (OFDM) technique, are gaining worldwide popularity due to their broad applications. For example, an OFDM based communication system may be used in a plurality of networks including Worldwide Interoperability for Microwave Access (WiMax) networks, Wireless Fidelity (Wi-Fi) networks, Wireless Broadband (WiBro) networks, etc.
The OFDM technique uses a plurality of closely-spaced orthogonal subcarriers to carry data. For example, the data may be allocated on a plurality of parallel data channels, one for each of the subcarriers. Each of the subcarriers may be modulated with a conventional modulation scheme, e.g., quadrature amplitude modulation, at a relatively low symbol rate. In addition, based on the OFDM technique, an inverse fast Fourier transform (IFFT) may be performed on OFDM symbols representing the data on a transmitting side, and a fast Fourier transform (FFT) may be performed to recover the OFDM symbols on a receiving side.
Signals including the OFDM symbols are transmitted through a communication channel from the transmitting side to the receiving side. In reality, the communication channel may have an effect on the signals when the signals are transmitted through the communication channel. For example, when propagating through the communication channel, the signals may be significantly attenuated at a certain frequency band or a certain period of time. As a result, data transmission may suffer from channel fading at the frequency band or the period of time, and reliability of data transmission may be reduced.
To enhance the reliability of data transmission, traditional resource randomization methods have been used to provide time and frequency diversity, and to average out interference signals from the transmitting side. For example, for a base station and a mobile station that are configured to communicate based on IEEE 802.16m standard, resource randomization may be performed at different levels of granularity, such as a tile level or a resource unit level. As a result of the resource randomization, data that would otherwise be transmitted at adjacent time or frequency resources may be transmitted at nonadjacent time or frequency resources. Such transmission may provide time and frequency diversity and reduce signal interference. Accordingly, the reliability of data transmission may be enhanced.
Data transmission with a relatively long transmission time interval (TTI) may call for or be improved by resource randomization methods that may provide time and frequency diversity. For the purpose of illustration, TTI is a parameter relating to encapsulation of data from higher layers into frames for transmission on a radio link layer and may refer to the length of an independently decodable transmission on a radio link.